1. Field of the Invention
The present invention relates to a station for reading and/or writing in a memory of a chip including an electronic circuit, in particular a gaming chip, said station including a system for storing said chip and a communication unit adapted to exchange information with said memory via an antenna arrangement when said chip is disposed in said storage system. The antenna arrangement includes first and second antennas comprising first and second loops, respectively. It is understood that in the remainder of the description the expression “storage system” is to be interpreted in the widest possible sense and covers in particular chip racks, boxes, and trays, as well as gaming, change or cash tabletops, in gaming rooms or casinos, and including chip sorting devices, and any surface or volume adapted to receive stacked or loose chips permanently or temporarily.
2. Description of the Prior Art
The expression “gaming chip” or “casino chip” means any disk-shaped or plate-shaped article representing a value, possibly a nominal value. Chips are generally fabricated from rigid and scratch-resistant plastics materials and carry patterns varying in design and color to form a more or less complex decoration to reduce the risk of falsification and/or fraudulent reproduction. Some chips incorporate an electronic circuit including a memory for storing information concerning the chip, in particular a number or an identifier and its numerical value. Chips equipped with electronic circuits including a memory are also referred to as “electronic memory chips” and “electronic circuit chips”. Different designs of chips have electronic circuits including PROM, EEPROM, or even microprocessors with associated memory.
The chip storage system, for example racks, are conventionally used to store chips at the cashier's window and/or at the gaming tables. A rack contains chips exchanged for money, for example chips or plates with different face values, cash, etc. It is also possible to take from the rack the chips necessary to pay out winning plays and to put into the rack chips collected from losing plays. The number of chips in a rack varies and consequently the overall value of the chips evolves over time.
To facilitate monitoring the chips contained in the rack and in and out movements of the chips, in order to achieve better control of those movements and thereby combat fraud more effectively, patent application WO 97/30414 proposes to provide the rack with columns for storing chips and reading and/or writing means able to communicate with the chips stored in said columns. The reading means include ferrite antennas at the top of the column or loop antennas disposed slantwise under the columns, although the latter do not have such good performance. Devices of the above kind give good results especially with ferrite antennas for a range of working frequencies from 125 kHz to 140 kHz. However, good results are more difficult to achieve at higher frequencies, for example 13.56 MHz or 2.45 GHz (the corresponding reduction in the number of turns in the antenna integrated into the chip commensurately reducing the resistance to interference caused by radiation from the ferrite antennas in the rack).
Moreover, storing chips in columns or stacks that are prepositioned prior to the writing and/or reading operations is not acceptable or appropriate in some applications, in particular for the closed storage area usually referred to as the “chip float” of American Roulette tables, for example. At this location, the chips must be stackable in different vertical stacks on the gaming table top, with no particular order or specific location.
From the patent EP 0 740 818, the person skilled in the art also knows of reading and/or writing stations including a gaming, change or cash tabletop carrying an antenna in the form of a spiral conductive layer printed on an insulative support and connected to a communication unit. The conductive layer of the antenna defines a central internal transmission area. The communication unit can exchange information with chips laid flat on the transmission area, including stacked chips.
As in the case of the chip racks mentioned above, exchanges with a chip via the antenna are effected “without contact”, by means of radio waves modulated at frequencies that are usually around 125 kHz to 140 kHz. Communication conventionally requires that the chip not be “on edge”, i.e. oriented parallel to the magnetic field generated by the conductive layer. The chip is preferably laid flat on the tabletop, and thus perpendicular to the magnetic field generated by the conductive layer of the antenna. Anticollision algorithms enable the communication unit to read/write all of the chips in one or more stacks.
The above type of antenna, although well suited to checking a chip or one or more stacks of chips (possibly comprising up to 20 chips) has the disadvantage of having a read/write shadow area at the internal boundary of the conductive layer, commensurately reducing the diameter of the central transmission area, for example an annular shadow area from 2 cm to 2.5 cm wide for a conductive layer with an outside diameter of 8 cm. What is more, the conductive layer of the antenna cannot be made wider at will. This is because a minimum ratio must be respected between the surface area of the antennas of the chips and the surface area of the conductive layer of the antenna.
In practice, it is considered that an antenna conductive layer must not be able to receive more than ten stacks of chips.
There is therefore a requirement for a reading and/or writing station having a large storage area or volume able to communicate reliably at high frequencies, with a memory in an electronic circuit chip disposed anywhere in the storage area.